1. Field of the Invention
This invention relates to rotating moles used in well hydrablasting work, and more particularly, to a slow rotating mole powered by a mud pump and driven through a wobble gear speed reducer.
2. Description of the Prior Art
The buildup of materials on the inside of pipelines and well casing or tubing is a common problem. It is known that many wells in some areas have buildup problems severe enough to eventually plug the tubing, and this problem may occur in both production and injection wells. Pipelines have similar problems.
Common compounds causing such buildup problems are barium sulfate, silicates, calcium carbonate, calcium sulfate, carbonate, sulfate, silica, water scale with hydrocarbons, coke tar, coke and complexes, wax and complexes, paraffins, sludges, muds and gels.
Many different methods have been used to remove material buildup. For example, one method of dealing with paraffin buildup is to melt the paraffin with hot oil. Hot oil units heat crude oil, and the heated oil is circulated into the well. Hot water has also been used to melt or remove paraffin and also to remove salt. While in many cases this technique is successful, it does have the disadvantage of requiring considerable energy to heat the oil or water, and it is not useful in removing other materials which will not melt from the heat or which are not water soluble.
Chemicals may also be used to dissolve paraffin deposits. This may eliminate the problem of heating, but the chemicals may require special handling because they are usually highly flammable and toxic.
Other methods to remove buildup include Dyna-Drills run on coiled tubing, milling with jointed tubing, acid washing, and broaching with a wireline.
To avoid the problem of removal of buildup by hot oil or water or by chemicals, jet cleaning was developed to utilize high pressure liquids to remove the materials by erosion. Coiled tubing service companies have performed jet cleaning jobs for many years. Generally, these jobs have been limited to removing mud cake, paraffin or packed sand. The jet cleaning tools of this type are usually made of heavy wall mechanical tubing with a plurality of holes of various diameters drilled in a symmetrical pattern around the tool. Water is used as the cleaning media. Job results were usually unpredictable. All of these techniques have achieved limited success, and it has been necessary on many occasions to change out the production tubing string. Accordingly, there is a need to efficiently and thoroughly clean material buildup in well casing or tubing.
The Otis "HYDRA-BLAST".RTM. system was developed to address these problems by providing an economical means of cleaning buildup deposits from downhole tubing. This system utilizes high pressure fluid jet technology in conjunction with the economy and efficiency of coiled tubing. The "HYDRA-BLAST".RTM. system includes an indexing jet cleaning tool, an in-line high pressure filter, a surface filter unit, a circulation pump with tanks and a coiled tubing unit. It also utilizes a computer program to design the actual cleaning jobs for any particular situation. The optimum jet size and number, retrieval speed and number of passes is calculated to accomplish a successful job, and this is particularly important in trying to remove harder materials such as the harder barium compounds. In general, this system may be described as a water-blasting system which directs high pressure streams of water against the buildup to remove the material by the eroding or cutting action of moving fluid.
In a typical application of the "HYDRA-BLAST".RTM. system, the operator uses a cleaning tool which usually utilizes a downward stream to cut into the material as the tool is lowered into the tubing. This portion of the tool is not particularly well adapted for removing large amounts of buildup along the walls after the tool is free to pass therein. So, the original down-blast tool is removed from the well, and an additional trip is made with a side-blast jetting head designed specifically for the purpose of providing jets directed against the buildup on the walls of the tubing. Reciprocation of the tool is usually necessary for thorough cleaning. This two-step process works well for short or moderate length buildup areas, but it is not particularly well adapted for extremely long buildup areas because it is difficult to rotate and reciprocate the tool to cover such an area. Also, without the ability to rotate, a large number of nozzles will be needed to provide good coverage which will increase flow and pressure drop due to fluid friction. This reduces the efficiency of the jets. Therefore, a need exists for a tool with low pressure drop which can be used to blast a long area of buildup and which needs only one trip into the wellbore and does not retrace its path.
The rotating mole system of the present invention solves this problem by providing a tool which rotates slowly as it is lowered into the tubing, so that it provides a complete 360.degree. path of jetted fluid as it is moved longitudinally. Very few jets are required for this tool. This configuration also makes the tool well adapted for use in pipeline cleanout where a long path is frequently present.